1. Field of the Invention
The present invention is directed to a fiber collimator and more specifically to a fiber collimator for use in an optical transmission system and/or an optical sensor system.
2. Technical Background
Collimation is a known process by which divergent beams of radiation or particles (e.g., light rays) are converted into parallel beams. Laser diode (LD) collimating lenses are commonly used in laser beam printers, bar code scanners and sensors. In addition, fiber collimators are widely used in a variety of optical applications (e.g., optical filters). Due to the recent increase in demand for fiber collimators as a basic building block, to be used with other components, in wavelength division multiplexed (WDM) systems, minimizing the fiber collimator reflective insertion loss has become increasingly important.
Commercially available dual-fiber collimators have typically utilized an individually aligned gradient-index (GRIN) microlens with fibers. These GRIN microlenses have generally been produced by an ion-exchange process and normally provide high coupling efficiency and have been utilized as collimators for laser beam printers, bar code scanners, optical isolators, circulators and digital versatile disc (DVD) players, as well as miniature objective lenses for medical/industrial endoscopes.
Planar microlens arrays (PMLAs) are two-dimensional GRIN-type lens arrays that integrate ion-exchange technology and photolithography for accommodating a plurality of fibers and lens array. By diffusing ions through a photolithographic mask into a glass substrate, numerous microscopic lenses can be formed in various sizes and patterns. Commercially available PMLAs are available with swelled lens surfaces, which tend to increase coupling efficiencies in transceiver applications, or with flat surfaces, which typically simplify collimation with fiber arrays. PMLAs have been used in liquid crystal projectors, three dimensional data processing and two dimensional laser diode (LD) coupling to fibers. Other manufacturers, such as Rochester Photonics Corp., have produced aspheric collimating microlenses that are intended to replace GRIN-type microlenses in collimating applications. Optical surface grinding, polishing, or molding are possible steps used to make the curved surfaces of generally aspheric microlenses.
However, when accommodating off-axis rays, the effectiveness of GRIN-type PMLAs and collimating arrays incorporating aspheric collimating microlenses are highly dependent on the configuration of the fiber collimator array. As such, it is important to configure the fiber collimator array to reduce insertion loss and internal reflections.
An embodiment of the present invention is directed to an optical fiber collimator in an optical system, which includes a pair of optical fibers having emitting or receiving cleaved planes to provide a substantially uniform angled side surface for forming a prescribed angle relative to the optical axis of the optical system. The emitting or receiving surfaces of the pair of optical fibers are disposed coplanarly in the object plane of the optical system for sharing the optical axis and separated from each other and from the optical axis on the same object plane. Optically coupled to the pair of fibers, a microlens has a sloped rear surface opposite a rotationally symmetric microlens surface which together with a cylindrical outer surface bound a volume having a homogeneous index of refraction. The pair of fibers are positioned near the focal plane containing the optical axis of the microlens for the generation or reception of collimated beams at the prescribed angle relative to the optical axis of the microlens.
According to an aspect of the present invention, the microlens comprises a wedged rod lens having a single refractive surface.
Additional features and advantages of the invention will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing the invention as described in the description which follows together with the claims and appended drawings.
It is to be understood that the foregoing description is exemplary of the invention only and is intended to provide an overview for the understanding of the nature and character of the invention as it is defined by the claims. The accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute part of this specification. The drawings illustrate various features and embodiments of the invention which, together with their description, serve to explain the principals and operation of the invention.